Advances in plant breeding methodology combined with increasing expenditures on breeding and increasing intensity of the improvement of seed quality imply that the price of seeds is constantly growing. Therefore, they are sold by the piece in the form of so-called seed units. This mainly concerns the seeds of sugar beet, canola and numerous species of vegetables.
Stimulation of seeds is a process of bringing the seeds to such a level of moisture that allows for the start of physicochemical processes in seeds, which lead to activation of embryo metabolism, but is not sufficient to break the layers surrounding the embryo by the elongating radicule. Stimulated seeds sown into the soil, having completed the pre-germination stage, move faster to the phase of proper germination, as well as growth and development of a young plant (seedling) than seeds which were not prepared in this manner. This can significantly shorten the period of emergence, which is particularly important during spring frosts, drought or excessive soil moisture, as well as on easily encrusted soils. Even and uniform germination of seed generation in diverse environmental conditions achieved in this manner is also important. Many years of research confirmed that accelerated, even by one day, and uniform germination can have a significant impact on the increase in the quantity and quality of crops, and thus measurable economic gain.
The essence of all existing stimulation technologies is to provide control of the quantity of water and rate of its absorption by seeds, and subsequently to subject them to a process of slow drying at room temperature. In order to control water absorption in the stimulating process, priming of seeds with a strictly defined amount of water or use of osmotic solutions, such as polyethylene glycol or inorganic salts, are applied.
Based on the publication (Gimenez-Sampaio T., Sampaio N. V., Souza R. H. V. de. 1997. Increase in germination and rate and emergence under low temperatures of maize (Zea mays L.) seeds subjected to osmotic preconditioning, Revista Cientifica Rural 2/1: 20-27), it is known that stimulation of corn seeds in a PEG 6000 solution at a concentration of 100 or 150 g/L of water, or in a 0.3 and 0.1% KNO3 solution for 10 days, improved their germination capacity under laboratory conditions by 35%. The germination capacity of seeds and their vigour also increased after priming in a solution of calcium salts at a concentration of 10 mmol/L.
Patent specification PL 207240 discloses a method for accelerating the germination of sugar beet seeds, wherein the seeds are mixed with natural zeolites or synthetic zeolites saturated with water, and after a defined period of imbibition in the presence of moist zeolites, the seeds are allowed to dry at room temperature and 60% of air humidity. Stimulation of sugar beet seeds to germination in the presence of zeolites is possible thanks to their sorption characteristics—they easily absorb water and easily liberate it in a continuous manner. An increase in the efficiency of this method was obtained by interrupting the stimulation process, drying the seeds and re-stimulation (i.e. stimulation—drying—stimulation and another drying) according to patent PL216893. According to this method, the seeds are mixed with zeolite, incubated at a temperature of 15-22° C. for 1-8 hours, depending on the vigour of stimulated seeds, then the process is interrupted, the seeds are separated from the zeolite and dried to a moisture of 7 to 30%, and subsequently, the seeds are mixed with zeolite again and stored at a temperature of 15-22° C. for 18-24 h. It is postulated that desiccation stress occurred as a result of drying the seeds causes the secretion of plant hormones activating a cascade of reactions leading to accelerated and uniform germination.
There are reports indicating that metal nanoparticles can be used to stimulate plant growth, although there is still no information related to their influence on seed germination itself. Thus, based on patent application RU2463757, it is known that it is possible to treat seeds of agricultural plants before sowing with a colloidal solution containing: silver (Ag) nanoparticles in the form of ions, dioctyl sodium sulfosuccinate, quercetin and ammonia. Before sowing, the seeds are sprayed with a solution of a concentration of 0.0047%, at an amount of 10 dm3/mg of seeds. Once germination was completed, the seeds prepared in this manner produced plants characterised by a larger size. The description documented the effect of the product on species such as: corn, wheat, oat and barley. Stimulation of plant growth using a solution containing Ag nanoparticles is also disclosed in patent application WO2014062079, but in this case, they are connected with polyhexamethylene biguanide or polyhexamethylene guanidine, which are known for their antibacterial activity. In turn, the summary of patent application KR20020034794 presents a process for application of gold (Au), silver (Ag) an copper (Cu) ions on seeds, characterised in that seeds such as rice, beans and corn are dried to reduce their water content, and subsequently, they are placed in distilled water between electrodes selected from a silver, gold and copper electrode for 5 h to allow deposition of metal particles on the grains. According to the declaration contained in the summary of the description, seeds prepared in this manner are less vulnerable to damage caused by bacteria, due to the known biocidal characteristics of the applied metals.
The above-mentioned applications of nanoparticles and metal ions are associated with the biocidal activity of these metals. These methods include providing silver, gold or copper nanoparticles on the seed surface, which contributes to the reduction of the negative effects of bacterial activity after sowing seeds into the soil, and thus increases the number of germinated, vigorous seeds, which subsequently develop young, healthy seedlings. As a consequence, it leads to an increased agricultural crop. These are the methods of a so-called: normal spray or, as in the latter described case, a complicated and expensive electrolytic method. Furthermore, known methods and products are related to nanoparticles in ionic form. Moreover, between the electrodes, not only metal ions but also an electromagnetic field can be active. Therefore, it is not entirely clear what the stimulating effect of plant growth is related to.
Publication J. Nawaz et al.: “Seed Priming A Technique” International Journal of Agriculture and Crop Sciences, vol. 6, no. 20, 1 Jun. 2013, p. 1373-1381 discloses a technique of seed priming in which increasing a level of moisture surrounding a seed initiates the physiochemical processes of germination. Use of copper and silver nanoparticles to stimulate grain and vegetable crops is disclosed by S. N. Maslobrod et al.: “Stimulation of Seed Viability by Means of Dispersed Solution of Copper and Silver Nanoparticles”, 1 Jan. 2013, p. 21-22. Publication Quoc Buu Ngo et al.: “Effects of nanocrystalline powders (Fe, Co and Cu) on the germination, growth, crop yield and product quality of soybean (Vietnamese species DT-51)” (Advances in Natural Sciences: Nanoscience and Nanotechnology, vol. 5, no. 1, 28 Feb. 2014, p. 15016-1) discloses a method of pre-sowing treatment of dicotyledonous soybean seeds in which the seeds are treated with a solution of zero valence nanoparticulate cooper, iron or cobalt.
However, the application of nonionic metal nanoparticles in the process of stimulating plant seeds so as to accelerate and equalise germination is not known.